1. Historical Data

Lyudmila Boyanova

Discovery of Helicobacter pylori by Marshall and Warren in 1982 was the start of a real revolution in the gastroenterology with a strong impact on medicine as a whole. In the 1870s, despite some reports on spiral bacteria in gastric tissues, stress and diet were thought to be the only causes of peptic ulcers. In 1979, Warren evaluated Campylobacter-like organisms (CLOs) in inflamed gastric tissues and in 1982, his co-worker, Marshall, isolated the bacteria. However, the discovery was initially met with much disagreement. For this reason, in 1985, Marshall performed self-inoculation by CLOs and proved their ability to cause gastritis. Originally called Campylobacter pyloridis and then corrected to Campylobacter pylori, the bacteria were renamed again due to taxonomic data as Helicobacter pylori in a new genus, Helicobacter. In 2005, Warren and Marshall were jointly awarded the Nobel Prize in Physiology or Medicine. Since the year of H. pylori discovery, various invasive and non-invasive diagnostic tests, susceptibility testing methods and treatment regimens for the infection have been developed and then improved. Participation of H. pylori in the pathogenesis of gastric cancer and MALT lymphoma has been proven. Moreover, H. pylori has been associated with several extragastric diseases. The enormous genetic diversity of the bacteria and their numerous virulence factors have been revealed and genomes of many strains have been sequenced. Presently, chronic gastritis and peptic ulcers are treated as bacterial infections by antibiotics combined with acid inhibitors. Improvement in eradication has been obtained by triple, quadruple, rescue, sequential or other regimens. The gift that Marshall and Warren's discovery has given to human medicine has been the consequent detection of the link between chronic bacterial infections and malignancy and, fascinatingly, the option to heal a tumour (as MALT lymphoma) by treating the associated microorganisms. However, at present, the treatment of H. pylori infection is not easy and still no vaccines are available for prophylaxis. Although the global rate of H. pylori infection is gradually decreasing, the antibiotic resistance of the bacteria is growing sharply in many countries. Regrettably, despite the fact that infection is often asymptomatic, H. pylori still infects half of the global human population and every fifth infected subject can develop severe disease. Therefore, it is important to stress that in the field of pathogenesis, epidemiology, diagnosis, prophylaxis and treatment of the infection, there are still approaches to be optimised and many questions to be answered.

2. Genus Helicobacter

Lyudmila Boyanova

The Helicobacter genus belongs to class Epsilonproteobacteria, order Campylobacterales, family Helicobacteraceae and already involves >35 species. Recently, new gastric (Helicobacter suis and Helicobacter baculiformis) and enterohepatic (Helicobacter equorum) species have been reported. Helicobacter pylori is of primary importance for medicine, however, non-pylori Helicobacter species (NPHS), which naturally inhabit mammals (except humans) and birds, have been detected in human clinical specimens. NPHS encompass two (gastric and enterohepatic) groups, showing different organ specificity. Importantly, some species such as Helicobacter hepaticus, Helicobacter mustelae and, probably, Helicobacter bilis exhibit carcinogenic potential in animals. NPHS harbour many virulence genes and may cause diseases not only in animals but also in humans. Gastric NPHS such as H. suis (most often), Helicobacter felis, Helicobacter bizzozeronii and Helicobacter salomonis have been associated with chronic gastritis and peptic ulcers in humans and, importantly, with higher risk for MALT lymphoma compared to H. pylori. Enterohepatic species e.g., H. hepaticus, H. bilis and Helicobacter ganmani have been detected by PCR in but still not isolated from specimens of patients with hepatobiliary diseases. Moreover, NPHS may be associated with Crohn's disease, inflammatory bowel disease and ulcerative colitis. The significance of avian helicobacters (Helicobacter pullorum, Helicobacter anseris and Helicobacter brantae) also has been evaluated extensively. NPHS such as Helicobacter cinaedi and Helicobacter canis can cause severe infections, mostly in immunocompromised patients with animal exposure. Briefly, the role of NPHS in veterinary and human medicine is increasingly recognised. However, despite the growing interest in the possible association between NPHS and the chronic hepatobiliary or intestinal diseases in humans, more studies are still required to prove the suggested association. Several other topics such as isolation of still uncultured species, antibiotic resistance and treatment regimens for NPHS infections and, last but not least, NPHS pathogenesis and possible carcinogenesis in humans should be additionally evaluated.

3. Microbiology and Characteristics of H. pylori

Lyudmila Boyanova

H. pylori are Gram-negative spiral and microaerophilic bacteria that undergo coccoid transformation under hostile conditions. The coccoids and bacterial biofilms may participate in the transmission of infection. Specific H. pylori characteristics such as its enormous genomic diversity, helical morphology, acid acclimation, Krebs cycle and lipopolysaccharide indicate the extreme adaptation of the bacteria to the gastric mucosa. Modern methods such as comparative genomics, transcriptomics and proteomics provide a deep insight on H. pylori genomic diversity and its expression according to the severity of the disease. Methods to diagnose the infection are invasive e.g., rapid urease test (RUT), histology, culture and molecular methods or less invasive such as string test, or non-invasive such as serology, urea breath test (UBT), stool antigen test (SAT) and some molecular methods. Choice of the test depends on the test characteristics e.g., type, preparation, accuracy, protocol, cut-off, availability and price, and on many patient characteristics, which indicate the likelihood of the infection. Recently, non-invasive methods such as immunoproteomics, new SATs and improved UBT and SAT protocols have been reported. Significance of anti-CagA antibodies for the risk of severe diseases has been highlightened. For the same purpose, a new test for serum pepsinogens and anti-H. pylori antibodies has been introduced. Recent molecular methods have been implemented to detect H. pylori and its resistance to both macrolides and quinolones or to spot non-invasively clarithromycin resistance. Advances have been made also in the invasive methods. In vivo histology has been suggested and, importantly, an operating link for histological estimation of gastric cancer risk (OLGA staging) has been published. However, further studies are strongly required on important issues, among them are applications of the present, or development of new, non-invasive tests for detection of H. pylori resistance to antibiotics, improvement of test accuracy in specific patient groups, use of most reliable biomarkers for severe diseases and strategy for H. pylori screening and eradication.

4. H. pylori Virulence Factors

Lyudmila Boyanova

H. pylori infection outcomes strongly depend on the strain virulence. H. pylori displays enormous genetic diversity by frequent mutations, intra- or intergenomic recombinations and natural transformation, and additional phase variations by slipped-strand mispairing. H. pylori spiral shape, urease, motility, lipopolysaccharide (LPS) and outer membrane adhesins enable the establishment of the infection. H. pylori genetic diversity and induced immunomodulation contribute to the infection chronicity. Prevalence of virulence factors varies according to the patient disease, ethnicity, age and country. H. pylori VacA causes vacuolation, pore formation, disruption of endo-lysosomal activity, apoptosis in gastric cells and immunomodulation. CagA oncoprotein alters cell-signalling pathways and induces morphological changes, chromosomal instability, cell proliferation and apoptosis, interleukin (IL)-8 release and proto-oncogene activation. CagA type D EPIYA and increased number of C repeats have been linked to increased SHP-2 phosphatase activity and hence high risk for gastric cancer. In East Asia, nearly all strains have been highly virulent, carrying intact cagPAI, East Asian CagA and vacA s1/i1/m1 type, which can help to explain the high gastric cancer incidence there. Although the infection outcomes have shown strong association with cagA, cagPAI and vacA status of the strains, mainly in Western countries, the combined activity of all H. pylori virulence factors, involving also dupA, oipA, iceA, homB, babA, sabA, hopQ and other genes/gene status appears to be crucial for the infection pathogenesis. Tipα protein, HP-NAP, heat-shock-proteins, LPS mimicry and interaction with toll-like receptors influence the infection course as well. By the complex and well-coordinated interplay of its virulence factors, H. pylori adapts to the changing environment and can either increase or suppress the gastric inflammation. Moreover, microevolution of the virulence genes emerges in the individual patient over years. Briefly, the direct effects of H. pylori virulence factors and the chronic gastric inflammation can lead to the development of peptic ulcers or malignancy. Targeting the virulent strains in a country or region is important to explain better the clinical significance of some virulence factors and their interaction, to choose local diagnostic markers, to imply aggressive eradication strategies in the concerned patients and to provide new agents and improved regimens to control the infection.

5. Immunology of H. pylori Infection

Ivan Mitov

Helicobacter pylori infection induces almost all mechanisms of innate and acquired immunity. Different bacterial, environmental and host factors may influence the balance between the protective role of the immune mechanisms and their role in gastric mucosal damage, respectively, the possibility of lifelong asymptomatic colonisation of gastric mucosa or clinical manifestation of H. pylori infection. Bacterial virulence factors stimulate Toll-like and Nod-like receptors to induce innate and adaptive cell mediated and humoral immune response. Balance of Th1/Th2 response is of great importance in host protection and in pathogenesis of H. pylori-mediated diseases. The polarised Th1 response is not sufficient to clear the bacteria. Moreover, a predominant activation of Th1 cells plays a key role in tissue damage. Th2 response appears to be protective against gastric inflammation. Cytotoxic activities of T cells are important for the outcome of H. pylori infection. Protection due to anti-H. pylori humoral, local and systemic immune response is minimal. Furthermore, the antibodies may promote colonisation of gastric mucosa.

6. Vaccines

Ivan Mitov

An effective vaccine is needed to improve the success of anti-H. pylori therapy. Cooperative action of cell-mediated, humoral and molecular responses is necessary for effective protection against H. pylori. Vaccines against H. pylori can be used as prophylactic vaccines to prevent the infection or as therapeutic vaccines to cure the infection, to improve the eradication success of standard regimens or to reduce the bacterial density in the gastric mucosa and the risk for emergence of antibiotic resistant strains. In recent years, many attempts, using various H. pylori antigens such as urease, CagA, HP-NAP, HspA or combinations, many adjuvants and different routes of immunisation have been made to create vaccines against H. pylori infection. Although some attempts are promising, no effective and safe vaccine against H. pylori is currently available for humans. New directions for immunisation with the use of DNA, living vectors, microspheres etc. are currently under evaluation. The vaccination plan and the groups who should receive vaccination are still to be determined but the vaccination will be useful, especially in developing countries.

7. Epidemiology of H. pylori Infection

Lyudmila Boyanova

H. pylori causes the second most common chronic bacterial infection in humans. As a result of the childhood-acquired and usually life-long (unless eradicated) infection, about 12-24% of the H. pylori positive subjects develop severe diseases e.g. peptic ulcers or gastric malignancy. In developed countries, the infection usually spreads intrafamilially; however, in developing countries or underdeveloped rural areas, it can be acquired often extrafamilially or via environmental contamination, leading to higher infection prevalence and greater intrafamilial diversity of the strains there. Infected mother and older siblings are important factors for H. pylori transmission to children. The transmission routes are oral-oral (by saliva), which prevails in the developed world, faecal-oral (person-to-person or by contaminated water, or maybe food), mainly in the developing countries or gastro-oral (by vomiting and regurgitation). Role of viable but not culturable coccoid forms and biofilms appears to be important. Oral H. pylori seems to be associated with combined oral and gastric infections, probably more often in the developing countries. However, PCR accuracy for detection of extra-gastric H. pylori needs improvement. As a whole, the infection prevalence is still high in countries/groups with poor socio-economic status. In many developing countries, ≥50% of children and ≥70% of adults have been H. pylori positive vs. only <15% of children and ≤20-40% of adults in most developed countries. Detection of anti-CagA antibodies has been used to spot infections by virulent strains and the importance of East Asian CagA testing has been stressed. Both reinfection and infection clearance also have been reported, mainly in children, although in high-prevalence countries, the infection clearance is unimportant. Many risk factors for the infection mirror poor socioeconomic status and a strong birth cohort effect. Both dietary and environmental factors are likely to modify the infection prevalence and should be further evaluated. In brief, improved hygiene and living conditions, urbanisation and growing antibiotic use for H. pylori and many other infections, all have led to a decrease in both infection and reinfection rates in the developed countries and, already, in some developing countries. However, the infection still affects every second person worldwide. Moreover, many important questions on the infection transmission routes and reservoirs still need elucidation.

8. H. pylori-associated Diseases

Borislav Vladimirov

Helicobacter pylori plays a main role in the development of gastritis all over the world. In addition, it is well known that H. pylori infection is associated with many nonmalignant and malignant gastrointestinal and extra-gastric diseases. H. pylori remains one of the most common causes of peptic gastro-duodenal ulcers, gastric mucosa associated lymphoid tissue (MALT) lymphoma and gastric cancer. In recent years, many clinical data have been collected about the relationship between H. pylori infection and gastro-oesophageal reflux disease (GORD), nonsteroidal anti-inflammatory drug⁄acetylsalicylic acid-induced gastric injury and functional dyspepsia as well as about pathogenetic mechanisms of these correlations. There are also evidences confirming the role of genetic differences in host and bacterial factors and the role of environmental factors. Recent data have shown a decline in incidence and prevalence rate of peptic ulcer related to H. pylori. For patients with functional dyspepsia, eradication of H. pylori offers a modest but significant benefit. An inverse relationship between H. pylori infection and reflux oesophagitis, and Barrett oesophagus has been also confirmed. Despite of the controversial results, eradication of H. pylori infection has been recommended for nonsteroidal anti-inflammatory drug- and acetylsalicylic acid-users as well as for patients treated with antiplatelet therapy. The beneficial effects of H. pylori eradication on MALT lymphoma and on the prophylaxis of gastric cancer have been proven. On the other hand, an increasing amount of evidence for extra gastric manifestation of H. pylori infection has been shown.

9. H. pylori Resistance to Antibiotics

Lyudmila Boyanova

H. pylori resistance to antibiotics emerges most often from point mutations but also from efflux mechanisms, natural transformation, altered membrane permeability and, probably, β-lactamase. The resistance, especially that to clarithromycin and quinolones, often causes treatment failures. For this reason, if national or regional primary resistance rates are ≥15-20% for clarithromycin and ≥40% for metronidazole, the agents should be avoided for primary therapy of the infection unless susceptibility testing of the strains is carried out. Clarithromycin resistance-associated A2143G point mutation most often predicts eradication failures. Moreover, heteroresistance in H. pylori strains has been reported for metronidazole, clarithromycin, amoxicillin and quinolones. From <10% to >37% of the strains exhibit mixtures of genotypes. Importantly, both clarithromycin and quinolone resistance rates have grown sharply in many countries and multidrug resistance has been found in <5% in Europe and >14% in Brazil and South Korea. High primary resistance rates to clarithromycin (20->40%) and fluoroquinolones (20->33%) have been reported mostly in developed countries. Conversely, high primary resistance to metronidazole (≥76%), amoxicillin (6->30%) and tetracycline (≥15%) has been observed in some developing countries. Primary resistance and its evolution often depend on the country and national antibiotic consumption, patient characteristics such as age, sex, disease, prior antibiotic use and comorbidity, strain characteristics such as virulence as well as other factors. Post-treatment resistance rates have been usually much higher, often >3 times for clarithromycin and clarithromycin + metronidazole and ≥1.5 times for metronidazole and quinolones, compared with those of the primary resistance. In brief, a worrying evolution of antibiotic resistance in H. pylori and disturbing multidrug resistance hamper more and more the success of the eradication of the infection. Knowledge on current H. pylori resistance patterns and evolution at global and local levels is highly important to show the efficacy or need for changes in treatment regimens and to improve the overall eradication success that also means the cure of the individual patient.

10. Treatment of H. pylori-associated Diseases

Borislav Vladimirov

Treatment of Helicobacter pylori infection remains a significant clinical problem despite the extensive research on the topic over the last 25 years. For H. pylori eradication, combined regimens of non-antibiotic (bismuth compounds and/or proton pump inhibitors) and usually two antibiotics are used. The antibiotic choice may involve amoxicillin, clarithromycin, metronidazole, tetracycline, levofloxacin, rifabutin and furazolidone. A number of factors such as duration of treatment, choice of antibiotics, new drug combinations, improved patient compliance and novel agents may help to improve the eradication rates. In this chapter, data on triple, quadruple, sequential and rescue therapeutic regimens are discussed. However, H. pylori resistance to antibiotics, poor patient compliance and host genetic polymorphism can strongly reduce the success of eradication. Recent data have shown that the rates of eradication have decreased worldwide. In the last years, many new drugs and combinations have been applied with aims to raise the eradication rates to more acceptable levels but more evidence is needed to support the routine use of the new antibiotics and modified treatment regimens for eradication of H. pylori.

11. Non-antibiotic Agents in the Treatment of H. pylori Infection

Lyudmila Boyanova

As standard regimens for the eradication of H. pylori infection often fail owing to antibiotic resistance or low patient compliance, there is an increasing need for new drugs such as non-antibiotic agents (NAAs) or optimised treatment regimens. Anti-H. pylori activity has been detected in vitro by many NAAs such as lactobacilli, Saccharomyces boulardii, lactoferrin, green tea, garlic, propolis, broccoli, resveratrol, plant oils etc. Many NAAs have been active against both antibiotic susceptible and resistant H. pylori strains. So far, cell line, animal or clinical trials have shown H. pylori eradication, although often low, using NAAs alone e.g., black caraway, garlic, green tea, turmeric, broccoli and mastic gum. Combinations of standard regimens with NAAs such as lactobacilli, S. boulardii, turmeric, Korea red ginseng, N-acetylcysteine and vitamin C have improved the eradication often by >10% and most of them have reduced the side effects of the regimens. Advantages of some NAAs are their anti-adhesive, anti-urease, anti-inflammatory and anti-tumour effects and bactericidal activity on H. pylori. Moreover, anti-adhesive NAAs can prevent H. pylori colonisation or reinfection. In addition, aspirin, monoclonal antibodies, redox protein inhibitors and synthetic antimicrobial peptidomimetics have been evaluated as applicants for therapeutic intervention. Synergy between NAAs is a very attractive topic, which should be evaluated, however, with caution. To choose an agent, it is necessary to consider the source, safety or toxicity, dose-depending deleterious effects and allergenicity of some NAAs as well as their quality control and evidence-based trials. At present, we await further studies, especially clinical trials, to suggest the choice, dosage, start time and duration of administration aiming at the routine use of the NAAs. In conclusion, NAAs probably carry greater than the expected potential for prophylaxis or adjuvant therapy of H. pylori infection and can help to control the rising bacterial resistance to antibiotics.